Recording oscillographic apparatus



Jajn. 9,1940'.

' I I A RECORDING OSGILLOGRAPHIC*APPARATUS A Filed Jan. 1957 Patented Jan. 9, 1940 UNITED STATES RECORDING OSCILLOGRAPHIC APPARATUS William E. Pakala, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh,v Pa., a lcoi-poration of Pennsylvania Application January 21, 1937, Serial No. 121,597

11 Claims.

My invention relates to apparatus for recording variable quantities such as voltages, currents. temperatures, speeds or torques, for example, and particularly to such apparatus which may be put into operation at a given instant of time and which will thereafter make an accurate record of the variable quantity under observation as it existed for some time prior to the given instant of time.

In its more specific aspects, the invention relates to oscillographic apparatus of the type in which a record oi' the variable quantity under observation is temporarily stored in some form of retentive medium, such that at the instant of starting the permanent oscillographic record, the variable quantity can be recorded for a time interval preceding the instant of starting. As examples of the retentive media heretofore proposed in the art for such applications, may be mentioned electrical networks or artificial lines in which are variable quantities are temporarily stored as travelling Waves, air columns in which the variable quantities are stored as sound waves, and rotating discs of magnetically retentive material on which a temporary magnetic record is made.

The above-mentioned expedients, although satisfactory for recording major variations of the variable quantity, introduce distortion of the wave form because of the effects of attenuation. In order to avoid distortion of wave form in such apparatus, it is necessary that the retentive medium have a negligible frequency error, and that it produce the same time delay `for all frequencies. That is to say, the ratio of the voltage, mechanical force or other variablev which affects the retentive medium, to the current, ldisplacement or other effect produced in the medium, must be substantially constant at all frequencies;

and also, the time delay between the application I of the voltage, mechanical force or other variable and the appearance of the variable from which a record is made, must be constant for all frequencies. With such a retentive medium, the fundamental and all harmonics of the variable quantity under observation would be reproduced in correct ratio and correct relative phase position, so that no distortion would be produced.

It is, accordingly, an object of my invention to provide a novel oscillographic recording device in which 'the variable quantity under observation can be recorded, without distortion, for a period of time preceding the disturbance which initiates the permanent recording operation.

Other objects of my invention will become evident from the following detailed description taken in conjunction' with the accompanying drawing, in which:

Figure 1 is a diagrammatic view of a recording oscillograph embodying my invention; and

Fig. 2 is a graphical record illustrating the operation of the invention.

In accordance with my invention, the desired tion, is impressed. In this way arecord oi' the variably quantity, in the form of bound electric charges, is produced. By making the resistance of the electric circuit negligible, the time constant RC of the circuit becomes negligible, and the increments of dielectric receive their final value of charge substantially instantaneously, thereby avoiding distortion of wave form. The time'lag of the capacitive recording device is fixed by the speed of rotation and is constant for all frequencies. Although my invention may be embodied'in various structural forms, I prefer to provide separate small capacitors as the dielectric increments, and to control the connections of these capacitors by means of a commutator.

Referring to Fig. 1 in detail, the capacitive recording device l comprises a rotor 2 arranged to be driven at substantially constant speed by any suitable driving'means such as a synchronous motor 3. The`rotor 2 comprises a plurality of small vcapacitors 4, a few of which are shown diagrammatically in Fig. 1, and a rotating commutator 5, such as is usually provided in a direct-current machine. Each of the capacitors 4 is connected to an individual bar of the commutator 5, and the remaining terminals of the capacitor 4 are connected to a suitable conductor of common potential, such as a slip ring 8, or may be grounded on the machine frame.

The slip ring 6 is engaged by a stationary slip ring brush 1, and the commutator 5 is engaged by three stationary angularly displaced brushes 8, 9 and I0. The brush 8 may be termed a charging brush, inasmuch as its function is to supply a charge to each of the condensers 4 in succession. The brush 9 serves to discharge the condensers 4 preparatory to a recharging operation by means of the brush 8. "Ihe brush' I 0 serves to transfer a delayed indication of the charges 2 impressed on the condensers I' by the brush l, to suitablerecording apparatus which will be hereinafter described.

The brushes 1 and 8 are connected to an input electric circuit I'I having terminals I2, upon which a voltagedependent upon vthe variable ratus may be set forth as follows. The rotor 2 is quantity under observation, is impressed.

The output brush I and the slip ring brush 1 are connected to a suitable recording oscillog-raph I3, which may be of any of a number of forms known in the art. In the form shown, the oscillograph I3 consists of a cathode-ray tube I4, and a photographic camera I8 mounted in aposition to photograph the' image projected on the screen of the cathode-ray tube Il. Therecording oscillograph I3 is vprovided with a suitable release device I8 for initiating the making of a permanent record. In the form shown. the release device I6 consists of an electromagnetic shutter opening device for the camera I8. It- .will be understood that upon operation of the release device I6, the camera shutter opens and thereafter automatically closes after a time delay determine'dby an adjustment of the camera I 8.

The cathode-ray tube Il consists of an evacuated envelope having suitable apparatusl (not shown) for projecting a beam of electrons from a cathode I8, between ak pair of electric iield plates I9 and a pair of sweep plates 20,'to a suitable screen I1 which becomes luminous at the point `where the electron beam impingesv A device 2I is provided for energizing the sweep plates 20 in accordance with the remaining variable to be recorded on the oscillographic record. In somel cases the device 2I may be a current transformer or other current responsive device so that the curve traced on the screen I1 will be a function of current and voltage. In

' other cases, however, the device 2I may be a source of alternating voltage of constant magnitude but variable frequency, for causing the image on the screen -I1 to include as many cycles of the voltage impressed on the plates I8 as may be desired. It will be assumed that the device 2l is a sourceof adjustable sweep frequency voltage, such l as commonly provided with cathode ray tubes.

The electromagnetic release device I8 is connected in the output circuit of a suitable gasillled electric dischargedevice 22 of the so-called grid-glow or 'Ihyratron type. The electric discharge device 22 is provided with a control electrode 23, which serves, when properly biased, to prevent a discharge between the anode and cathode of the device 22. A` bias battery 2l is provided for biasing the control electrode 23 negatively with respect to the cathode of the electric discharge device 22, to such a voltage value as to block the discharge device 22 during all normal conditions. The control electrode 23 is also connected to suitable apparatus for rendering the device 22 conducting upon the occurrence of a predetermined condition, such as a reverse current flow of fault magnitude, or other abnormal disturbance, which is to initiate a recording operation of ythe oscillograph I3. In the embodiment shown, the apparatus takes the form of a current transformer 21, which for purposes of illustration will be assumed as'energlzed in accordance with the anode current of a rectifier (not shown), in such'manner that the initial halfcycle of induced voltage during an arc-back will neutralize the bias potential applied. to the control electrode 23, and cause a discharge current to traverse the device 22. A' suitable source 23 of plate .voltage'is includedin series with the principal electrodes of the electric discharge device 22 andthe electromagnetic release device I8, in I accordance with the usual practice. 6

Theoperation of the above-described appaing that an alternating voltage is impresed upon 1o the input terminals I2, as each segment of the commutator 3 passes over the brush 8, the condenser I connected thereto, is charged to a voltage equal to the instantaneous voltage impressed upon the terminals I2. at the instant that the l segment leaves the trailing edge of the brush 8. The condensers 4 travelling from the brush 8 toward the brush I0 accordingly carry a point-forpoint record of the voltage wave impressed upon the terminals I2. As the commutator segments travel from the brush 8 in the direction Vof the arrow 28 around to the brush I0, a time delay is introduced, dependent upon the synchronous speed of the motor 3 and the angular displacement between the brushes 8 and I0.

Upon arriving at -the brush I0, each commutator segment causes the electric field plates I9 to be charged to a voltage substantially equal to that upon the condenser 4 connected to the segment. In this way, the voltage upon the electric eldplates I9 is caused to follow a succession of stepped values, the initial point of each of which corresponds exactly to a point on the original voltage Wave impressed upon the terminals I2.

Referring to Fig. 2, in which voltage is plotted as ordinates and time as abscissa, it. will be seen A that by making the time during which a single y commutator segment is in contact with the brush III small, the stepped wave maybe made to more 40 and more closely approach the exact form of the voltage wave impressed upon the input terminals I2. I have found that for a motor speed of 1800 R. P. M.. and a commutator having a number of segments of the order of several hundred, the 4g wave form appearing on`the screen I1 bears no visible irregularities and appears to be a smooth curve. In some cases, however, it is desirable to have thewave form appear stepped or dotted, so that the distance betweenA dots, or the length of stepped portions, mayfbe taken as an indication of time. For this purpose, the motor speed or number of commutator bars' may be reduced, or the wave amplitude increased sufliciently to break up the smooth curve. Witha broken wave form, the cycle timing wave, sometimes required for oscillographic work, becomes unnecessary. Such a broken wave, also, may be used to record three variables on the same trace; for example, current and voltage may appear as Cartesian coordinates of the trace, and time as the number o'f dots `appearing between various points on the trace.

The shutter of the camera I5 is normally closed, but upon the occurrence of the predeterminedfcondition which causes the electric discharge device 22 to become conducting, the camera shutter is open, thereby making a photograph` record of the image appearing upon the screenv I1 at the instant of shutter opening. I have found that it is practicable to open the camera shutter in a time interval of the order of .3 to .4 of a cycle of 60 cycle supply.

Because of the 'time lag resulting from the travel of each commutator segment from the brush Il to the brush I0, the image appearing upon 7| the screen il at the instant of shutter opening, represents the voltage which was impressed upon the terminals I2. at some time previous to the instant of shutter opening. For the particular values given above, the time delay would be of the order of 11/2 cycles of a 60-cycle supply, so that if the sweep frequency supplied by the source 2| were such as to embrace, say, three cycles of the 60cycle supply, the image appearing upon,

the screen Il would consist'of approximately-11A cycles of the variable quantity under observation, previous to the disturbance which initiated oper-1 ation of the release device I6, and approximately 11/2 cycles of the variable quantity following the disturbance.

It will be obvious that various other forms of oscillographic apparatus or other recording apparatus may be substituted for the specific recording oscillograph I3 shown. It will also be obvious that any other phenomena than voltage may be recorded by this apparatus, by merely translating the quantity to be observed to a voltage and impressing it upon the terminals I2.

vThe numerical values given above are arbitrarily chosen for purposes of illustration, and it' will be obvious that the invention may be practiced with numerical values of an entirely different order.

I do not intend that the present invention shall be restricted to the specific structural details, arrangement of parts, or circuit connections herein set forth, as various modifications thereof may bo effected without departing from the spirit and scope of my invention. I desire, therefore,

that only such limitations shall be imposed as are indicated in the appended claims.

I claim as my invention: 1. In apparatus for recording a variable quantity, an electric circuit to be energized in accordance with the quantity to be recorded; a capacitive storing device having a plurality of electric Acharge-retaining portions, said storing device comprising means for successively including said portions in said circuit for variable energization in accordance with instantaneous values of said electrical condition; and means for translating the successive charges bound on said portions intoa graphical representation of said variable quantity.

2. vIn apparatus responsive to a predetermined condition for automatically recording a variable quantity for a time interval commencing at least as early as the start of said condition, an electric circuit to be energized in accordance with the quantity to be recorded; a capacitive storing device having a plurality of electric charge retaining portions, said storing device comprising means for successively including said portions in said circuit for variable energlzation in accordance with instantaneous values of said electrical condition; and means effective upon the occurrence of said predetermined condition for translating the charges bound on said portions during said time interval into a graphical record of said variable quantity.' l

3. In apparatus responsive to a predetermined condition for automatically recording a variable quantity for a time interval commencing at least as early as the start of said condition, an electric circuit to be energized in accordance with the quantity to berecorded; a capacitive storing device having a plurality of electric charge-retaining portions, said storing device comprising means for successively including said portions in said circuit in a predetermined cycle, and removing the charges from said portions prior to a repetition of the cycle; and means for translating the successive charges bound on said portions into a graphical representation of said variable quantity.

4. In apparatus for recording a variable quantity, an electric circuit to be energized in accordance with the quantity to be recorded; a capacitive storing device comprising 'a plurality of capacitors, and commutating apparatus for cyclically connecting each of said vcapacitors in said circuit for variable energization in accordance with instantaneous values of said electrical condition; and means for translating the successive changes on said capacitors into a graphical representation of said variable quantity.

5 In apparatus for producing a delayed oscillographic record of a variable quantity, an electric circuit to be energized in accordance with the quantity to be recorded; an oscillograph; a plurality of capacitors;and commut'ating apparatus for connecting each of said capacitors in rotation in said circuit and for thereafter connecting each of the charged capacitors i'n rotation to said oscillograph.

y 6. In apparatus responsive to a predetermined condition for automatically recording a variable quantity for a time interval commencing at least as early` as the start of said condition, an electric circuit to be energized in vaccordance with the quantity to be recorded; a plurality of capacitors; commutating apparatus for connecting each of said capacitors in rotation in said circuit; and means effective upon the occurrence of said condition for translating the charges bound on said capacitors during said time interval to a graphical record of said variable quantity.

7. In apparatus responsive to a predetermined condit1on for automatically producing an oscillographic record of a variable quantity for a time interval commencing at least as early as the start of said condition, an electric circuit to be energized in accordance with the quantity to be recorded; a recording oscillograph having a release device effective to initiate a recording operation; a plurality of capacitors; commutating apparatus for connecting each of said capacitors in rotation in said circuit and for thereafter connecting each of the charged capacitors in rotation tc said oscillograph; and means responsive to said predetermined condition for operating said release device.

8. In apparatus responsive to a predetermined condition for automatically producing an oscillographic record of a variable quantity for a time interval commencing at least as early as the start of said condition, an electric circuit to be energized in accordance with the quantity to be recorded; a recording oscillograph having a release device effective to initiate a recording operation; a rotary device comprising a plurality of capacitors mounted for rotation, a rotating commutator having a plurality of bars each connected to one of said capacitors, and stationary brushes in engagement with said commutator, said stationary brushes including a charging brush connected to said circuit and an output brush connected tosaid oscillograph; said output brush being angularly displaced from said charging brush, motive means for driving said rotary device; and means responsiveA to said predetermined condition for operating said release device.

9. In apparatus for recording a variable quantity, an electrical circuit to be energized in ac- 7l fao oordance with the quantity to be recorded; a discontinuous energy storing device having a piurality of individually effective energy storage elements of similar characteristics, said storing device comprising means for successively energizing said elements from said circuit. in a timed sequence, to variable degrees dependent upon the instantaneous values of said electrical condition; and electroresponsiue means for translating the individual quantities of energy stored on said elements into a graphical succession of indicia following said sequence, each of said indicia incating a quantity corresponding to the energy storage in one of said elements, whereby the variations of said variable quantity as a function of time may be determined by the incremental variations of magnitude of successive indicia.

10. In apparatus responsive to a predetermined condition for automatically recording a variable quantity for a time interval commencing at least as early as thestart of said condition, an electric circuit to be energized in accordance with the quantity to be recorded; a capacitive storing device having a plurality of discrete charge-retaining elements of similar characteristics, said storing device comprising means for successively including said elements in said circuit, in a timed sequence, for variable energization in accordance with instantaneous values of said electrical condition; and means effective upon the occurrence of said predetermined condition kfor translating aisance the charges bound on said elements during said time interval into a graphical succession of distinguishable indicia following saidy sequence, whereby the variations of said variable quantity as a function of time may be determined by the recorded; a recording oscillograph having a release device effective to initiate a recording operation; a capacitive storing device having a plurality of discrete charge-retaining elements of similar characteristics, said storing device comprising means for successively including said elements in said circuit, in a timed sequence, for variable energization in accordance with instantaneous values of said electrical condition and for thereafter connecting each of the charged ele-4 ments to said oscillograph in the order of said timed sequence at intervals sufllcient to'produce distinguishable oscillographic records of individual charges on said elements, and means responsive to said predetermined condition foroperating said release device.

wnmm n. PAKALA. 

